Nickel plating



Patented Jan. 10, 1950 Robert Horace Rogge, Evanston, Ill., and EdwardJudson Roehl, Little Silver, N. .1 assignors to The InternationalNickelCompany, Inc., New York, N. Y., a corporation of Delaware No Drawing;Application January 5, 1946, Serial No. 639,426. In Canada September 6,1945 3 Claims. (01. 204-49) The present invention relates to a processfor producing electro-deposits of nickel and more particularly, to aprocess for producing. thick, ductile and adherent electro-deposits ofnickel without streaks on foundation metals, especially on zinc-basecompositions, such as zinc and zinc alloys.

Heretofore, the most'commonly used processes for direct nickeling ofzincand zinc alloys were the so-called high-sulfate nickel bath and thetype of bath disclosed in the Tuttle U. S. Patent No. 2,069,566 assignedto the Zialite Corporation. The high-sulfate bath comprises nickelsulfate, a chloride such as ammonium chloride or sodium chloride, boricacid and large quantities of sodium sulfate. The sodium sulfate permitsdeposition of nickel directly on zinc without the formation of blackstreaks on moderately low current density areas. The deposit, however,tends to be brittle and sometimes it is necessary to deposit a moreductile nickel coating over the thin highsulfate nickel bath coating.However, in such cases, a good bond between the two nickel coatings isnot always obtained. Furthermore, the useful current density rangebetween burning and black streaking in the deposit from the highsulfatenickel bath is too narrow for many complicated shapes; the applicablerange for the high-sulfate nickel bath for depositing nickel directly onzinc being about 12 amperes to about 20 amperes per square foot. As thebondbetween the two nickel coatings is not always good, and as theuseful current density range of the high-sulfate bath is narrow, coppercoatings have largely taken the place of the high-sulfate nickel bathcoating, particularly when bright nickel is used as a second coat.Generally speaking, the high-sulfate nickel bath is used only to obtainthin nickel coatings.

The Zialite bath is also used for direct electronickeling of foundationmetals, particularly on zinc and zinc alloys. This bath, which hasunusual ability to cover recesses without streaking, contains nickel inthe form of complex pyrophosphates and citrates, and also containssodi-' um and ammonium sulfates, chlorides and free ammonia. The Zialitebath is normally operated at current densities of between 2 and 20amperes per square foot. Even though the Zialite bath has good throwingpower and a tolerance for zinc three or four times as great as prior artbaths for direct electro-nickeling of zinc and zinc alloys,nevertheless, the useful current density range of the Zialite bath isconsidered to be 65 narrow and the nickel deposits obtained therefrom onzinc and zinc alloys tend to be brittle.

As the aforementioned high-sulfate and Zialite baths, when used fordirect electro-nickeling of zinc and zinc alloys, deposit nickelcoatingsthat .tend to be brittle, and as the useful current denadherentnickel plating substantially without streaks is obtained over-a widerange of current density without burning and streaking of the depositand without necessity for using intermediate ductile coatings such ascopper. In our novel and improved process, an easily controllableelectro-plating bath having a simple composition is employed underplating conditions, including hydrogen ion concentration and currentdensity, which are properly correlated with the bath composition.

It is an object of the present invention to provide a process forproducing a thick, ductile and adherent electro-deposit of nickelsubstantially without streaks directly on metal foundations.

It is another object of the present invention to provide a process forproducing thick, ductile and adherent electro-deposits of nickelsubstantially free. from streaks directly on metal foundations,particularly zinc-base compositions i. e. zinc and zinc alloys.

Still another object of the present invention is to provide a processfor producing a thick, ductile and adherent electro-deposit of nickelwithout streaks directly on metal foundations, particularly zinc-basecompositions, by employing a novel electro-plating bath having a simplecomposition.

A further object of the present invention is to provide a process forproducing thick, ductile and adherent electro-deposits of nickelsubstantially without streaks directly on metal foundations,particularly zinc-base compositions, by use of an electro-plating bathof simple composition that can be operated with desired results over awide range of current density.

It iswithin the purview of the present invention to provide a processfor producing a thick, ductile and adherent electro-deposit of nickelsubstantially without streaks directly on foundation metals particularlyzinc-base compositions, without the necessity of employing anintermediate ductile coating such as copper.

It is still a further object of the present invention to provide anelectro-plating bath for the electro-deposition of a thick, ductile andadherent nickel plating without streaks directly on metal presentinvention contemplates the electro-deposition over a wide range ofcurrent density of a thick, ductile and adherent deposit of nickelsubstantially without streaks directly on suitable foundation metals,particularly zinc-base metal compositions such as zinc and zinc alloys,by use of a novel aqueous plating bath prepared from nickel chloride,tartaric acid and ammonium hydroxide. The invention also contemplatesthe operation of the novel bath embodied in the present invention underplating conditions, including hydrogen ion concentration and currentdensity, properly correlated with the bath composition. The presentinvention further contemplates the electro-deposition of a thick,ductile deposit of nickel without streaks directly on foundation metals,especially zinc-base compositionssuch'as zinc and zinc alloys, andincluding zinc-base die castings, whereby the thick, ductile nickelco'ating obtained has good adhesion to the foundation metal and has notendency to peel ofi. More- 1;

over the novel bath employed by the present invention is extremelysimple in composition and can be readily controlled over a wide range ofcurrent density to obtain a nickel deposit that is thick, ductile,adherent and substantially free from streaks.

The nickel plating bath, employed by the present invention, as recitedhereinbefore, contains tartaric acid and nickel chloride in an aqueoussolution regulated to a desired pH value by addition of concentratedammonium hydroxide. It is not necessary to add any other ingredients tothe novel plating bath of the present invention to obtain therefromelectro-deposits of nickel directly on metal foundations, especiallyzinc-base compositions, that are thick, ductile, and adherent andsubstantially free from streaks when the novel bath is operated over awide rangeof current density.

The aqueous plating bath employed by the present invention is generallycontrolled within the following ranges of compositionand platingconditions:

Tartaric acid,'about to about '150 grains per liter Nickel chloride(NiClz-6H20), about 15 to about 100 grams per liter pH, about 5.0 toabout 7 .2

per sq. ft.

While the bath compositionsand-plating'conditions given hereinbeforehave'beenfourid satisfactory, inczarrying the present invention intopractice, we prefer to employ compositions and plating conditions withinthe following ranges:

Tartaric acid, about to about grams per liter Nickel chloride(NiC12-6H2O), about 20 to about 40 grams per liter pH, about 5.3 toabout 6.2

Current density, about 15 to about amperes per sq. ft.

In the compositions given hereinbefore for the novel tartaricacid-nickel chloride plating bath, the pH is regulated to the desiredvalue by addition of concentrated ammonium hydroxide.

While it is stated herein that the aqueous plating bath provided by thepresent invention is principally abath made by adding nickel chlorideand tartaric acid to water and then regulating the pH to the desiredvalue by an addition of ammonium hydroxide, it is to be understood thatsmall amounts of minor constituents, impurities and incidental elementsand/or compounds maybe present, although not essential for obtaining thedesired results; e. g. the bath may contain small amounts of zinc,oxalates, phosphates, sulfates, iron, copper, lead, cobalt, and alkalimetals generally introduced as minor constituents and/or impurities ofthe principal in- "gredients, i. e. tartaric acid, nickel chloride andammonium hydroxideof the plating bath. While small amounts 'ofingredients other than tartaric acid, nickel chloride and ammoniumhydroxide may not detrimentally affect the nickel electrod'eposit, wehave found that the presenceof sulfate ion, if present in substantialquantity in the plating bath, 'detrimen'tal'ly affects the resultsobtained as compared to those obtained from 'an all-tartaric acid-nickelchloride-ammonium hydroxide bath. For example, when nickel sulfate isused to replace a substantial portion of the nickel chloride "content ofthe bath composition employed by the present invention, inferior*results are obtained as either no deposit or streaky deposits areproduced when the bath containing a substantial amount of sulfate ion isoperated (NiSO4 7H20) 'lhe acidic limits for the novel tartaric"acidnickel "chloride bath employed by'the presentinvention are criticaland must be maintained within about pH 5.0 to about pH 7.2 to obtain thedesired results in electro-d'epositing thick,

ductile and adherent nickel substantially free from streaks over a widerange of current density directly "on metal foundations especiallyzincbas'e compositions i. e.'zi-nc and zinc alloys. Althoughsatisfactory-results are obtained when the novel'el'ectro-pl'atingbath-of the present invention is operated within a pH range of 5.0 to7.2,

Current density, about 10 to about 90 amperes K we prefepto Operate thebath Wlthin a PH'r'ange of 5:3 to 6.2, as we have found that when the pHofthe novel'electro-plating'bath exceeds 6.3 there 'is a tendency forformation of'an insoluble film at the-anode. When the pI-Iof the noveleleotrm'pla'ting bath is'more alkalinethan about pH 7.2 conditions aresuch that there is a tendency for formation of colloidal nickelhydroxide. When the novel electro-plating bath of the present inventionis operated at a pH more acid than pH 5.0, conditions are such that azinc cathode surface is deleteriously attacked by the electroplatingbath.

As has been recited hereinbefore, the current density range generallyemployed by the present invention is generally controlled within aboutamperes per square footto about 90 amperes per square foot. Althoughthick, ductile and adherent nickel platings substantially free fromstreaks can be obtained on metal foundations, especially zinc-basecompositions, when current densities down to about 10 amperes per squarefoot are employed, we have found that at current densities of aboutamperes per square foot or lower the current efficiency is poor. Anincrease in the nickel concentration of the novel electroplating bathtends to offset this effect of a decrease in current efficiency so thatwith the baths having a high concentration of nickel, it is feasible tooperate the bath at about 10 amperes per square foot with desiredresults. As hereinbefore stated, the current density of about 90 amperesper square foot is generally employed as the upper limit of the currentdensity range. This upper limit of current density is determined byvoltage requirements, as for the anode to cathode spacing generally usedin commercial practice, a current density of about 90 amperes per squarefoot requires the full voltage of an ordinary plating generator.

In order that those skilled in the art may have a better understandingof the present invention the following illustrative examples are given:

Example I An aqueous plating bath was prepared having about 30 grams perliter of tartaric acid, about grams per liter of nickel chloride, andregulated to a pH of about 5.3 by addition of concentrated ammoniumhydroxide. At current densities of about to about 90 amperes per squarefoot, at a temperature of 100 F. and employing nickel anodes, thick,ductile and adherent electro-deposits of nickel substantially free ofstreaks were obtained when electro-plated directly on zinc surfaces.

Example II An aqueous bath was prepared having about 120 grams per literof tartaric acid, about 80 grams per liter of nickel chloride andregulated to a pH of about 6.2 by addition of concentrated ammoniumhydroxide. At a current density of about 45 amperes per square foot, ata temperature of about 100 F. and employing nickel anodes, thick ductileand adherent electro-deposits of nickel substantially free of streakswere obtained when electro-plated directly on zinc.

Example III An aqueous plating bath was prepared having about grams perliter of tartaric acid, about grams per liter of nickel chloride, andadjusted to a pI-I of about 5.3 by addition of concentrated ammoniumhydroxide. At a current density of about 10 to about 20 amperes persquare foot, at a temperature of about 100 F. and employing nickelanodes, a thick, ductile and adherent electro-deposit of nickel withoutstreaks was obtained when electro-plated directly on a zinc surface.

Example'I V An aqueous plating bath was prepared having 30 grams perliter of tartaric acid, about 20 grams per liter of nickel chloride, andregulated to a pH of about 5.3 by addition of concentrated ammoniumhydroxide. At a current density of about 20 amperes per square foot, andemploying nickel anodes, a thick, ductile, and adherent electro-depositof nickel without streaks was obtained when electro-plated directly on asteel surface.

In the art of nickel electro-plating, a nickel electro-deposit of about0.0002 inch or less is generally considered to be a thin deposit. Byemploying the process of the present invention, ductile electro-depositsof nickel substantially free from streaks can be obtained having athickness of more than 0.0002 inch, e. g., more than about 0.0005 inch.Moreover, by employing the process embodying the present invention,ductile nickel electro-deposits exceeding 0.001 inch can be obtaineddirectly on suitable foundation metals particularly zinc-basecompositions.

Although the present invention has been described with particularemphasis on zinc-base compositions, such as zinc and zinc alloys,including zinc-base die castings, the novel tartaric acid-nickelchloride bath embodied in the present invention may be employed toobtain thick, ductile, and adherent nickel electro-depositssubstantially free from streaks on other metal foundations, includingaluminum-base compositions, such as aluminum and aluminum alloys, copperbase compositions, such as copper alloys, and steel.

It will be apparent from the foregoing that the present inventionprovides a practical and satisfactory process for producing thick,ductile and adherent nickel electro-deposits without streaks directly onmetal foundations, especially zinc-base compositions. The novel bathembodied in the present invention is simple in composition, easy toprepare and has good stability. When employing the novel tartaricacid-nickel chloride bath, the plating conditions that may be employedare such that desired results are obtainable over a wide range ofcurrent density as nickel electro-deposits that are not objectionablefrom the viewpoint of streaking can be produced. The nickelelectro-deposits that are obtained are thick and ductile, as determinedby bend tests, and adhere well Without tendency to peel whenelectro-plated on metal foundations, particularly zinc-base compositionssuch as zinc and zinc alloys.

Although the present invention has been described in conjunction withcertain preferred embodiments thereof, those skilled in the art willunderstand that variations and modifications thereof can be made. Suchvariations and modifications are to be considered to be within thepurview of the specification and the scope of the appended claims.

We claim:

1. A process for electrodepositing nickel directly on zinc-base metalcompositions which comprises establishing a bath having a temperature ofabout F. and a pH within the range of about 5.3 to about 6.2, andcontaining tartrate ions in an amount equivalent to a tartaric acidconcentration of about 30 to about 50' grams per liter, nickel ions andchloride ions in amounts equivalent to a nickel chloride concentrationof about 20 to about 40 grams per liter, ammonium ions equivalent to theamount of ammonium hydroxide required to regulate the pH of said bath.within said range,. and the balance of the bath being essentially water,said bath be ing, substantially devoid. of sulfate ion, andelectrodepositing nickel. from said bath at a current density of about10 to about 90 amperes per square foot upon a zinc-base metalcomposition, whereby a thick, ductile and adherent nickel. platingsubstantially free from streaks is ob.- tained.

2. A process for electrodepositing nickel directly on zinc-base metalcathodes which comprises establishing a bath having a temperature ofabout 100 F. and a pH of about 5.3, and containingv tartrate ions in anamount equivalent to a tartaric acid concentration of about 30 grams perliter, nickel ions and chloride ions in amounts equivalent to a nickelchloride concentration of about 20 grams per liter, ammonium ionsequivalent to the amount of ammonium hydroxide required to regulate thepH of said bath to about. pH 5.3,. and the balance of the bath beingessentially water, said bath b.e ing devoid of sulfate. ion, andelectrodepositing nickel from said bath at a current density of about 10to about 90- amperes per square foot upon azinc-base metal cathode,whereby a. thick, ductile and adherent nickel plating substantially freefrom streaks is. obtained.

3. An electroplating bath adapted for direct nickel plating on zinc-basemetallicv materials which comprises. a water solution contain-- ingabout. 3.0 to about. 60 grams. per liter of tartaric. acid andabout 26'to. about 40; grams. per

- liter of nickel chloride to which has been added ammonium hydroxidesufficient to regulate. the pH of said bath within the range of about5.3.: to 6.2, the balance of the bath being essentially water, said bathbeing substantially devoid of sulfate, ion.

ROBERT HORACE ROGGE'. EDWARD JUDSON ROEHLL REFERENCES CITED.-

The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,069,566 Tuttle Feb. 2, 19-372,351,966 Hogaboom June 20, 1944 OTHER REFERENCES

1. A PROCESS FOR ELECTRODEPOSITING NICKEL DIRECTLY ON ZINC-BASE METAL COMPOSITIONS WHICH COMPRISES ESTABLISHING A BATH HAVING A TEMPERATURE OF ABOUT 100*F. AND A PH WITHIN THE RANGE OF ABOUT 5.3 TO ABOUT 6.2 AND CONTAINING TARTRATE IONS IN AN AMOUNT EQUIVALENT TO A TARTARIC ACID CONCENTRATION OF ABOUT 30 TO ABOUT 60 GRAMS PER LITER, NICKEL IONS AND CHLORIDE IONS IN AMOUNTS EQUIVALENT TO A NICKEL CHLORIDE CONCENTRATION OF ABOUT 20 TO ABOUT 40 GRAMS PER LITER, AMMONIUM IONS EQUIVALENT TO THE AMOUNT OF AMMONIUM HYDROXIDE REQUIRED TO REGULATE THE PH OF SAID BATH WITHIN SAID RANGE, AND THE BALANCE OF THE BATH BEING ESSENTIALLY WATER, SAID BATH BEING SUBSTANTIALLY DEVOID OF SULFATE ION, AND ELECTRODEPOSITING NICKEL FROM SAID BATH AT A CURRENT DENSITY OF ABOUT 10 TO ABOUT 90 AMPERES PER SQUARE FOOT UPON A ZINC-BASE METAL COMPOSITION, WHEREBY A THICK, DUCTILE AND ADHERENT NICKEL PLATING SUBSTANTIALLY FREE FROM STREAKS IS OBTAINED. 